1. Field of the Invention
The present invention relates to a lens barrel which is used with their lens groups collapsed in one mode, and with their lens groups extended to their predetermined positions in another mode.
2. Description of the Related Art
It has been strongly requested that image taking apparatuses such as digital still cameras and digital video cameras (hereinafter referred to as “digital cameras”) have enhanced photographic performance and portability. Against this background, some image taking apparatuses have a configuration in which: while in a non-photographic state, at least a part of the lens groups is retracted from its photographic position on a photographic optical axis, and the lens groups are collapsed inside a camera main body with distances among the lens groups reduced to a level less than the minimum necessary distances required for image taking as much as possible; and while in a photographic state, these lens groups are extended from the inside of the camera main body such that distances among the lens groups become long enough for image taking. In such image taking apparatuses, holding frames for holding the respective lens groups, except the retractable lens, are held by multiple telescopic movable lens barrel which are configured to be movable in the direction of the photographic optical axis with respect to the fixed barrel portion of the camera main body; and the holding frames are accordingly collapsible into and extendable from the camera body. These image taking apparatuses are suitable to be carried, because the lengthwise dimension (hereinafter also referred to as a “thickness dimension”) of the movable lens barrels in the direction of the photographic optical axis can be reduced by putting the lens barrel into the collapsed state.
However, these image taking apparatuses have a risk that a large load is caused on the connecting part between the movable lens barrels and the fixed barrel portion when an impact attributable to an external factor such as their fall or collision by other objects acts in the direction of optical axis of the movable lens barrels during a photographic state, that is to say, a state in which the movable lens barrels are extended.
Against this background, a lens barrel has been already known, in which: at least one of the retractable lens groups is held by a retractable lens holding frame configured to retract the retractable lens groups outside the inner diameter of the fixed barrel portion; and concurrently, the lens barrel is provided with a collision preventing piece for, when put into a photographic state, preventing the movable lens barrel from moving into the fixed barrel portion in the direction of the optical axis (see Japanese Patent Application Publication No. 2007-219121).
This collision preventing piece is made to move to a position in which the collision preventing piece comes into contact with the rear end surface of the movable lens barrel when the movable lens barrel is to be retracted toward the fixed barrel portion, because the collision preventing piece is made to advance toward the inside of the fixed barrel portion in conjunction with the advancement of the retractable lens holding frame from the outside of the fixed barrel portion onto the photographic optical axis. Thereby, the lens barrel makes it possible to inhibit the increase in an outer diameter of a fixed barrel portion without increasing the distances among the lens groups while collapsed, compared with the conventional configuration in which the lens groups are retracted to the inside of the fixed barrel portion. In addition, the lens barrel can prevent a large load from being caused on the connecting part between the movable lens barrel and the fixed barrel portion due to an impact produced by an external factor.
Nevertheless, the configuration of the above-mentioned conventional lens barrel is as follows. The collision preventing piece is designed to advance to the inside of the fixed barrel portion in conjunction with the advancement of the retractable lens holding frame from the outside of the fixed barrel portion onto the photographic optical axis. In addition, the collision preventing piece is configured to be retracted to the outside of the fixed barrel portion in conjunction with the retraction of the retractable lens holding frame from the photographic optical axis to the outside of the fixed barrel portion. This configuration is based on the prerequisite that the conventional lens barrel is provided with the retractable lens holding frame which moves in and out across the fixed barrel portion. This requires a drive source for the retractable frame in addition to the drive source for the movable lens barrel.
Furthermore, the above-mentioned conventional lens barrel makes it difficult to effectively reinforce an area corresponding to a location in which the connecting part between the movable lens barrel and the fixed barrel portion is provided, because the collision preventing piece restricts its set position to the vicinity of the retractable lens holding frame in the circumferential direction of the fixed barrel portion due to its use of the drive source for the retractable frame which is dedicated to the retractable lens holding frame.